Modeling nucleation and growth of zinc oxide during discharge of primary zinc-air batteries

Abstract

Metal-air batteries are among the most promising next-generation energy storage devices. Relying on abundant materials and offering high energy densities, potential applications lie in the fields of electro-mobility, portable electronics, and stationary grid applications. Now, research on secondary zinc-air batteries is revived, which are commercialized as primary hearing aid batteries. One of the main obstacles for making zinc-air batteries rechargeable is their poor lifetime due to the degradation of alkaline electrolyte in contact with atmospheric carbon dioxide. In this article, we present a continuum theory of a commercial Varta PowerOne button cell. Our model contains dissolution of zinc and nucleation and growth of zinc oxide in the anode, thermodynamically consistent electrolyte transport in porous media, and multi-phase coexistance in the gas diffusion electrode. We perform electrochemical measurements and validate our model. Excellent agreement between theory and experiment is found and novel insights into the role of zinc oxide nucleation and growth and carbon dioxide dissolution for discharge and lifetime is presented. We demonstrate the implications of our work for the development of rechargeable zinc-air batteries. Highlights• Modeling and simulating of VARTA button cell • Validation of galvanostatic discharge and lifetime analysis• Nucleation and growth of ZnO and its impact on discharge curve• Degradation due to carbonation of alkaline electrolyte (Birger Horstmann) promising candidates to fulfill this demand, because of their high specific energy density and the use of cheap and abundant materials. These batteries are open at the cathode and use atmospheric oxygen.Several metals, e.g., lithium, sodium, and zinc, are potential active anode materials in metal-air cells [1]. The high theoretical energy density of lithium-air batteries has stimulated a lot of research [2]. For aprotic electrolytes, the challenge is to influence growth mechanisms in order to maximize capacity, while maintaining sufficient reversibility [3,4,5,6,7,8,9]. Aqueous lithium-air batteries require a stable lithium conducting anode protection [10,11,12,13]. Non-aqueous sodium-air cells rely

A Review of Model-Based Design Tools for Metal-Air Batteries

“…The open-circuit voltage of a ZAB in 30 wt % KOH is 1.65 V. The high conductivity of the electrolyte, high mobility of OH -, and reasonable kinetics of the ORR give the cell a nominal discharge voltage of 1.2 V at current densities of circa 10 mA · cm −2 [55]. The molar volume of ZnO is 60% larger than metallic Zn, which causes the cell to expand during discharge.…”

“…The molar volume of ZnO is 60% larger than metallic Zn, which causes the cell to expand during discharge. Even so, ZAB button cells demonstrate a practical energy density on the order of 1000 Wh · L −1 [55]. …”

“…When the ZAB is operated in air, CO 2 can dissolve in the electrolyte and react with OH -to form CO 2 -3 [56]. This parasitic reaction reduces the conductivity of the electrolyte, slows down the cell reactions, and eventually kills the cell [55]. As such, the lifetime of alkaline ZABs is limited from the moment they are exposed to air.…”

“…This layer of porous ZnO is generally modeled as an additional mass transport barrier [55], slowing diffusion and migration of OH -to the electrode surface. Early models determined the passivation characteristics using the so-called Sand equation, an empirical expression linking current density, i, and passivation time, t, with constants, k and i e : i = kt 0.5 + i e .…”

“…More recently in 2017, Stamm, et al, implemented the effect of type I ZnO passivation in a continuum model by calculating the thickness of the ZnO shell and numerically solving for the species concentration at the surface [55], assuming Nernst-Planck transport across the barrier. These values were then used to calculate the Nernst potential and exchange current density of the Zn dissolution reaction.…”